How you stroked up 320is?
How you stroked up 320is?
Hi.If you want to do the 2.0liter 2.3 exept rods you must change also crunk?Can anyone tell me exactly the difference?Thanks
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france320isco
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HI ALL
If you go here http://www.realoem.com/bmw/partgrp.do?m ... 7259&hg=18
and you do a cross part search you will find that unfortunately to go for a 2.3 you have to buy crank, rods and pistons.
I was told that changing rods was sufficient to stroke up a 320is, but after real oem i'm not so sure
and you do a cross part search you will find that unfortunately to go for a 2.3 you have to buy crank, rods and pistons.
I was told that changing rods was sufficient to stroke up a 320is, but after real oem i'm not so sure
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winstontj
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- Location: 02129 (Boston, Massachusetts, USA)
I didn't even know that there was an s14b20 until I started coming to e21.net... Interesting...
A little engine background:
To stroke a motor you need to increase the stroke of the crankshaft. Every +1mm you increase the crank (I assume that the 2.0i s14 is a 135mm rod and 80mm stroke like the m10b20 but I could be wrong. Stock s14b23 connecting rods are 144.25mm) so if you increase the stroke to 81mm you are actually increasing your stroke by 2mm because you pull down 1mm and push up 1mm (remember there is an up stroke and a down stroke). So for every 1mm the gain is 2mm. If you move from 80mm stroke to 81mm stroke you will pull the piston and rod down 1mm further on intake stroke however on compression stroke you will also push the rod and piston up 1mm further into the head and valves (which is bad). We use different pistons to compensate for this. For simplicity we keep the same stock s14b20 connecting rod and we change from an 80mm stroke to an 81mm stroke
On the down stroke our stock rod pulls the piston down 1mm extra, on the up stroke it pushes it up 1mm extra. To compensate for this we relocate the piston wrist pin UP 1mm, which drops the piston DOWN 1mm. Now when we pull down on the intake stroke the piston pulls down 2mm extra (one from the crankshaft and one from the relocated wrist pin) but on the compression stroke the +1mm up on the crank is negated by the -1mm down on the piston wrist pin so we have a net of 0 meaning the piston comes to the same place but pulls down 2mm further - increasing stroke by 2mm for every 1mm change to the crankshaft.
The s14b23 crank is 84mm stroke (this I know) and the s14b25 crank is 87mm stroke. By going from s14b20 80mm to s14b23 84mm stroke we apply the same theory as above so we must relocate the piston wrist pin up the amount of the stroke increase, in this case 4mm. This gives us 8mm stroke increase and with a 95mm (i think) bore that is 300cc difference. The next thing engine builders look at is rod/stroke ratio - which is the ratio of the conecting rod to the stroke. On the s14b23 BMW chose the 144mm rod because it yields a rod/stroke ratio of ~1.68 which is considered by many to be ideal. If you change stroke at the crank you must also change piston wrist pin location. If you keep the 135mm rod (which is what I assume stock is) you will have a lower rod/stroke ratio of ~1.6 which means your piston speeds will be higher. as long as you are not racing or trying to rev up over 8,000rpm with your motor you should be OK using the s14b23 crank with stock s14b20 rods and get new pistons to match. I think that you would find cheaper pistons available with the 144.25mm stock s14b23 rod because the combination is so popular.
Hope that gives you something to chew on for a little while...
Short answer - when you change stroke by anything over +1 to +2mm you should expect to need new crankshaft, connecting rods and pistons.
A little engine background:
To stroke a motor you need to increase the stroke of the crankshaft. Every +1mm you increase the crank (I assume that the 2.0i s14 is a 135mm rod and 80mm stroke like the m10b20 but I could be wrong. Stock s14b23 connecting rods are 144.25mm) so if you increase the stroke to 81mm you are actually increasing your stroke by 2mm because you pull down 1mm and push up 1mm (remember there is an up stroke and a down stroke). So for every 1mm the gain is 2mm. If you move from 80mm stroke to 81mm stroke you will pull the piston and rod down 1mm further on intake stroke however on compression stroke you will also push the rod and piston up 1mm further into the head and valves (which is bad). We use different pistons to compensate for this. For simplicity we keep the same stock s14b20 connecting rod and we change from an 80mm stroke to an 81mm stroke
On the down stroke our stock rod pulls the piston down 1mm extra, on the up stroke it pushes it up 1mm extra. To compensate for this we relocate the piston wrist pin UP 1mm, which drops the piston DOWN 1mm. Now when we pull down on the intake stroke the piston pulls down 2mm extra (one from the crankshaft and one from the relocated wrist pin) but on the compression stroke the +1mm up on the crank is negated by the -1mm down on the piston wrist pin so we have a net of 0 meaning the piston comes to the same place but pulls down 2mm further - increasing stroke by 2mm for every 1mm change to the crankshaft.
The s14b23 crank is 84mm stroke (this I know) and the s14b25 crank is 87mm stroke. By going from s14b20 80mm to s14b23 84mm stroke we apply the same theory as above so we must relocate the piston wrist pin up the amount of the stroke increase, in this case 4mm. This gives us 8mm stroke increase and with a 95mm (i think) bore that is 300cc difference. The next thing engine builders look at is rod/stroke ratio - which is the ratio of the conecting rod to the stroke. On the s14b23 BMW chose the 144mm rod because it yields a rod/stroke ratio of ~1.68 which is considered by many to be ideal. If you change stroke at the crank you must also change piston wrist pin location. If you keep the 135mm rod (which is what I assume stock is) you will have a lower rod/stroke ratio of ~1.6 which means your piston speeds will be higher. as long as you are not racing or trying to rev up over 8,000rpm with your motor you should be OK using the s14b23 crank with stock s14b20 rods and get new pistons to match. I think that you would find cheaper pistons available with the 144.25mm stock s14b23 rod because the combination is so popular.
Hope that gives you something to chew on for a little while...
Short answer - when you change stroke by anything over +1 to +2mm you should expect to need new crankshaft, connecting rods and pistons.
Just to add that the 320is pistons can and should be kept. Actually they're an upgrade for the M3 e30 engine builders and this increases compression to around 12:1.
If you're using OEM cams it's a direct fit but if you plan using wilder cams just deepen the valve pockets around 1.5mm.
I advise you to deepen the pockets even if you're using the OEm cams for the simple reason that if you want to upgrade them later the pistons don't need to come out.
If you're using OEM cams it's a direct fit but if you plan using wilder cams just deepen the valve pockets around 1.5mm.
I advise you to deepen the pockets even if you're using the OEm cams for the simple reason that if you want to upgrade them later the pistons don't need to come out.